1. Field of the Invention
The present invention relates to a vehicle in which an engine is automatically stopped upon establishment of a predetermined engine stop condition and restarted upon establishment of a predetermined restart condition, and more particularly, to a control device of a vehicle for restarting the engine by engaging a predetermined clutch of an automatic transmission upon restarting.
2. Description of the Related Art
In order to reduce fuel consumption, emission of exhaust gas, noise and the like, a vehicle is known which is configured to automatically stop the engine under a predetermined stop condition, while waiting at a crossing, for example, as in Japanese Patent Application Laid-Open No. HEI 8-14076).
In the aforementioned vehicle, upon establishment of the restart condition reflected by a driver's intention to drive, for example, by depressing the acceleration pedal, it is necessary to restart the engine immediately.
However, if the automatic transmission is hydraulic, the cessation of the engine may suspend an oil pump driven by the engine. Accordingly, for example, the oil supplied to a forward clutch (a predetermined clutch) of the automatic transmission is drawn from an oil passage, thus reducing an oil (hydraulic) pressure. Therefore, the forward clutch for operating the transmission and a clutch brake for hydraulically switching a gear ratio will be temporarily released.
Upon establishment of the restart condition of the engine in the aforementioned state, the engine starts rotating, and a discharge pressure of the oil pump in the transmission is gradually increased. Then, when the hydraulic pressure for the operation becomes sufficient, the forward clutch is engaged (connected), for example, to a first gear or "speed." The connection of the clutch means that the oil drawn from the oil passage is supplied again through the oil passage. Accordingly, an unacceptably long time is required until the clutch is connected after restart of the engine. In this case, if the forward clutch is not quickly engaged, the acceleration pedal may be depressed while the transmission is effectively in a neutral state, such that the forward clutch may be engaged when the engine is at an elevated RPM, thereby creating a possibility of an engagement shock. There is a risk that such an engagement shock may give an uncomfortable feeling to an occupant as well as reduce a durability of the clutch.
Accordingly, in order to prevent the aforementioned effects, a technique has been disclosed wherein a large-sized accumulator is used to maintain the forward clutch in an engagement state, until the engine that has been automatically started is restarted.
Further, Japanese Patent Laid-Open No. HEI 9-39613 discloses a technique in which the fuel supply to the engine is suspended to keep the engine rotation at an idling speed by driving the motor generator, rather than stopping the engine operation completely, such that operation of the oil pump is not stopped.
However, the technique suggested in Japanese Patent Laid-Open No. HEI 8-14076 in which the forward clutch is kept in an engagement state with a large-sized accumulator when the engine is stopped, may cause other disadvantages owing to the accumulator, such as deterioration of a drain performance during shifting from a D (drive) position to an N (neutral) position thereby retarding the releasing speed of the forward clutch, or enlargement of the hydraulic control device size, for example.
Further, the technique disclosed in Japanese Patent Laid-Open No. HEI 9-39613 is able to reduce the fuel consumption, however, it may demand a large battery to store sufficient electric power to drive the generator, in spite of reduced fuel consumption.